Theoretical Study Of Photo-/Electrocatalytic Nitrogen Fixation And Carbon Dioxide Reduction

The conversion of carbon dioxide and nitrogen into value-added chemicals and fuels（e.g.,hydrocarbons,oxygenates,and ammonia）using photo-/electrocatalysts as an alternative to fossil fuels is an attractive strategy,which has received considerable attention from researchers worldwide.Although the photo/electrochemical conversion of nitrogen and carbon dioxide into chemicals and fuels has made exciting research progress in the past few decades,the yield and Faraday efficiency of products are not ideal due to the poor catalytic activity of the catalysts.To date,there is still no photo/electrochemical catalyst that meets the need for commercialization.Therefore,the design of efficient photo-/electrocatalyst has become a hot research focus.On the other hand,with the development of high-performance computers,first-principles-based density functional theory plays an increasingly important role in the research fields of computational materials science and computational chemistry,especially in the exploration of catalytic reaction mechanism and the design of new catalysts.Based on first-principles calculations,this thesis proposed number of strategies and new mechanisms to improve the efficiency of photo-/electro catalytic reaction:boosting N₂reduction through construction of the donor–acceptor of dual-metal sites;designing Cu₂S monolayer photocatalysts for highly selective CO₂ reduction into C₂H₅OH;proposing a covalency aided electrochemical mechanism for CO₂reduction.The main conclusions are summarized below:（1）Highly efficient photo-/electrocatalytic reduction of nitrogen into ammonia by dual-metal sites.In this work,we put forth a method to boost N₂ reduction reaction through construction of donor–acceptor couples of dual-metal sites.The synergistic effect of dual active sites can potentially break the metal-based activity benchmark toward efficient N₂reduction reaction.By systematically evaluating the stability,activity,and selectivity of 28heteronuclear dual-atom catalysts of M1M2/g-C₃N₄ candidates,Fe Mo/g-C₃N₄ is screened out as an effective electrocatalyst for N₂ reduction with a particularly low limiting potential of-0.23 V for N₂ reduction reaction and a rather high potential of-0.79 V for hydrogen evolution reaction.Meanwhile,Ti Mo/g-C₃N₄,Ni Mo/g-C₃N₄,and Mo W/g-C₃N₄ with suitable band edge positions and visible light absorption can be applied to N₂reduction reaction as photocatalysts.The excellent catalytic activity is attributed to the tunable composition of metal dimers,which play an important role in modulating the binding strength of the target intermediates.This work may pave a new way for the rational design of heteronuclear dual-atom catalysts with high activity and stability for N₂reduction reaction.（2）Selective visible-light driven highly efficient photocatalytic reduction of CO2 to C2H5OH by two-dimensional Cu2S monolayers.Herein,we demonstrate that two-dimensionalβ-andδ-phase Cu₂S monolayers are promising photocatalysts for the reduction of CO₂ into C₂H₅OH based on the density functional theory simulation.The calculated potential-limiting steps for the CO₂ reduction reaction are less than 0.50 e V,while those for the hydrogen evolution reaction are as high as 1.53 and 0.87 e V.Most strikingly,the C–C coupling only needs to overcome an ultra-low kinetic barrier of～0.30 e V,half of that on the Cu surface,indicating that they can boost the C₂H₅OH conversion efficiency greatly.Besides,these photocatalysts also exhibit satisfactory band edge positions and suitable visible light absorption,rendering them ideal for the visible light driven CO₂ reduction reaction.Our work not only provides a promising photocatalyst for achieving the efficient and selective CO₂ reduction,but also brings new opportunities for advanced sustainable C₂H₅OH product.（3）Synergistic effect of copper and boron dual active sites drives high-efficiency ethanol product.In this work,a covalency-aided electrochemical mechanism for CO₂reduction is proposed by embedding boron on copper surfaces,in which p-block dopants have a significant impact on modifying adsorbent intermediates and improving the catalytic activity.Herein,B atom not only provides empty and occupied orbitals to adsorb and activate CO,but also affords a large amount of charge to stabilize the C₂ intermediates.In addition,B atom can also adjust the oxidation state of nearby copper(Cu^δ+),and the synergistic Cu^δ+and B dual active sites act as O*adsorption site and C*adsorption site,respectively,leading to strong adsorption and activation of CO₂.First-principles calculations reveal that CO₂ can be reduced into C₂H₅OH with an ultralow potential of-0.26 V.This study provides new insights into CO₂ reduction,which offers a promising way for achieving efficient ethanol product.